Originally Posted by
warrenw
I recently did something similar, I arrived at SFO earlier than anticipated and was booked in P for SFO-LAX. I was able to take an earlier flight and still stay in first even though there was a waitlist. I didn't do it at the gate though, I went to customer service to process the change.
but was P available for the flight you got on? if so, then that doesn't really help with the question. If not available, a good follow up will be what booking class did you get booked into?